There is a growing movement, driven by both industry and academia, towards a new network control paradigm called Software-Defined Networking (SDN). In Software-Defined Networking (SDN), a control plane implements and maintains the control logic that governs the forwarding behavior of shared network switching elements on a per user basis. A logical network that is implemented for a tenant of a hosting system is a good example of an SDN. The virtual (logical) network of a tenant of the hosting system connects a set of data compute nodes (e.g., virtual machines, etc.) that are assigned to the tenant, to each other and to other virtual and/or physical networks through a set of logical switches and logical routers.
In some cases, a network control system manages the control plane using multiple levels of control entities using various systems. Communicating between a tuple-based control entity and a message-driven control entity poses many difficulties as the first relies on eventual consistency to generate output from input data, while the other requires a strict protocol and state machine.